Light cast on the role of microRNA on animal domestication

A molecular study into key domesticated animals, including the horse, has highlighted the role of microRNAs in our selective guidance of these species into the many breeds we see today.

If DNA is an orchestra, microRNA (miRNA) is the conductor – an important regulator of cell development in mammals. They are one of the main reasons why, even though the DNA of every cell in an individual (give or take a few) is the same, we are able to produce 200 different types of cell in a human body.

Research into miRNA at the Earlham Institute in England has shed light on our selectively guided evolution of domestic pets and farmyard animals.

The work, involving the horse, cow, pig, rabbit and dog, explored the similarities and differences between each species.

The results of domestication have been quite incredible. Over just a few thousand years of selective breeding, these creatures have been bred for specific characteristics, leading to a wide range of body shapes and behaviors across breeds.

Better understanding of the domestication process can lead to better, more sustainable food and a greater understanding of human diseases.

The institute’s Dr Luca Penso-Dolfin investigated these species’ brains, testicles, hearts and kidneys for clues into how miRNAs differ across all of these tissues, and how this might affect the evolution of gene regulation.

It turns out that recently evolved “new” miRNAs were particularly abundant in brains and testes. Some of these more recent miRNAs may well be linked to important domestication genes in dogs and cows – perhaps one of the drivers behind the fascinating diversity in dog breeds that have been produced.

“The evolution of different miRNAs in different species might lead to important changes in how genes are used and controlled,” Dr Luca Penso-Dolfin says.

“These modifications, which might happen both in space (different tissues) and time (for example, different developmental stages) are still not fully understood. Further research is needed to better clarify the role of miRNAs in the evolution of mammalian gene regulation.”

By comparing the five domestic animals in the study to a database of miRNAs, Penso-Dolfin was able to identify which miRNAs were “old” miRNAs, present across many mammal species, and which miRNAs had evolved more recently, in only one or a few species.

These “new” miRNAs were found to be more specific to certain tissues, with most found in the brain and the testes.

From the perspective of evolution, it looks like these “new” miRNAs have an important role to play in the emergence of novel traits, especially when looking at cows and dogs, and analysis of the genes that the miRNAs work on suggests that their gene targets are enriched for genes under artificial selection – so it appears that the team have found some miRNAs that are of importance to the domestication process.

Domestic mammals are of great economic and biomedical interest. A better understanding of gene regulation in these species might help shed light on some diseases common to humans.

The diseases presenting in dogs, for example, have many commonalities with those in humans. The pig’s high resemblance to human anatomy is of further interest. Moreover, some of these species (especially the cow and the pig) represent an important food source, meaning that the same discoveries might also be relevant for milk production, meat quality, and resistance to disease or stress.

Professor Federica Di Palma, director of science at the institute, said: “The study of small regulatory RNAs as crucial regulators of diverse biological processes is an exciting area of research that continues to open up new avenues to explore when it comes to unravelling the complex evolution of economically important traits.

“Understanding the roles of miRNAs and their co-evolution with target genes in domestication can help not only improve understanding of fundamental biological processes but will also help us to better understand key traits of domestication selection with important applications to food security.”

The better we understand how they develop, the more light we can shed on our own evolution – and perhaps answer many difficult questions on how to cure certain diseases.

The team now plans to scale the research up to compare domestic mammals with wild animals, to get an even greater understanding of the important mechanisms underpinning how we’ve managed to produce such a range of domesticated species with specialist characteristics.